AU611423B2

AU611423B2 - Process for obtaining acids and salts in dissolution by ion exchange resins

Info

Publication number: AU611423B2
Application number: AU13208/88A
Authority: AU
Inventors: Manuel Bravo; Manuel Olivo Gonzalez
Original assignee: Industrial Quimica del Nalon SA
Current assignee: EMPRESA NACIONAL DE FERTILIZANTES SA; Industrial Quimica del Nalon SA
Priority date: 1987-03-18
Filing date: 1988-03-17
Publication date: 1991-06-13
Anticipated expiration: 2008-03-17
Also published as: DE3808633A1; PT84807B; IL85745A; GR880100167A; KR880010825A; IL85745A0; IT8819825A0; MA21219A1; DK150588A; PT84807A; LU87168A1; NO881163L; SE8800974L; AR245018A1; ES2004570A6; GB2203964B; GB8806340D0; MX168146B; GB2203964A; NL8800684A

Description

THE COMMISSIONER OF PAltNI~ OUR REF: 53185 S&F CODE: 55783 MAIL O-r IC FFVE DOLLAR 5845/2 E l Iw I14 23 F Ref: 53185 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: Address for Service: Industrial Ouimica Del Nalon, S,A.

Avenida de Galicia, 31 33005 Oviedo

SPAIN

Empresa Nacional De Fertilizantes, S.A.

Prim, 12 28004 Madrid

SPAIN

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Process for Obtaining Acids and Salts in Dissolution by Ion Exchange Resins The following statement is a full description of this invention, best method of performing it known to me/us including the i 5845/3 patent were granted upon an application made by those employees.

JTA:61W r- 1 ION-EXCHANGE PROCESS The present invention relates to an ion-exchange process.

The present invention is based upon the utilisation of ion exchanging resins of a cationic or anionic nature, in order to make ionic changes with solutions, such as saline and acid solutions, and thus obtain solutions of other products.

A typical ion exchanging resin that can be used in the present invention is a copolymer of styrene and divinylbenzene sulphonate of macroporous structure, which appears as a solid in the form of spheres of a diameter close to 0.6 mm. Several companies manufacture these types of resins and they are available on the world market. Such resins resist the osmotic changes, originating from contact with -solutions of different concentrations, without experiencing physical changes which alter their form. They can pass from the acid form to the saline form and the reverse an indefinite number of times and maintain their structure. They can also resist the oxidising or reducing action of some solutions.

The styrene and divinylbenzene copolymer cationic ion exchanging resins are sulphonic acids and behave like a strong acid. When the resin is in contact with a solution of a salt, an acid/salt equilibrium is established which can t be represented by the reversible equation: j 30 RH KA RK HA in which "RH" is the resin in acid form; "RK" is the resin in saline form; is the cation of the salt in solution; is the anion of the salt in solution; and is the hydrogen ion or a cation other than the cation.

For the purposes of the present invention, and in accordance with established terminology, an ion exchanging resin is I'C 0^ JTA:61

W

said to be "charged" when it passes into the saline form and it is said to be "regenerated" when it passes into the acid form.

When an ion exchanging resin in acid form is available in a sufficiently high column form in an adequate receptacle and a solution of a salt, like potassium chloride (KC1), is made to circulate slowly though the immobile resin from bottom to top, exchange of ions takes place between the resin and the solution which tends to establish a physical-chemical equilibrium at each point of the column. As a consequence of the ion exchange, the solution becomes more acid as it advances through the resin until all of the salt is transformed into acid and the resin is charged with the corresponding cation. A zone is established within the column, above which there is present the resin in acid form and below which there is present charged resin. Thus, there is established within the column a gradient of concentration of salt which is lower towards the top of the column.

The established zone of ion exchange advances towards the top of the column as the solution of salt is introduced through the lower part, leaving behind the charged resin and generating at the front of it a solution of the acid corresponding to the salt, which is extracted though the upper part.

The concentration of the anion corresponding to the salt, which is introduced into the column, maintains itself practically constant in the whole column. However, there may be small variations due to the different degrees of solvation oe the resin in the acid and the saline media.

The height of the ionic exchange zone of the column depends on the affinity of the resin to the cation of the salt with respect to the hydrogen ion. The affinity is proportional to the volume and valency of the cation.

i 3 If the direction of circulation of the solutions which flood the resins is inverted by feeding acid solution though the upper part of the column and extracting salt through the bottom, the zone of ion exchange is shifted downwards (i.e.

in the same direction as the solution) and the resin is regenerated in reversible form. In this case, the width of the zonie of ion exchange is different and will be dependent upon the different affinity of the resin to the cations, such as H and K.

Therefore, according to the behaviour described, if a saline solution is passed in an ascending direction and at an adequate speed through a column of a regenerated cationic resin of sufficient height, the resin is progressively charged in an ascending direction within the column due to the establishment of an ionic exchange zone, which zone is a defined volume of resin within the column. The dimensions of the zone are dependent upon the type of cations to be exchanged between the resin and the solution. As the ionic exchange zone shifts within the column, and in the same upwards direction as the solution, there is produced an acid corresponding to the salt which is introduced.

The quantity of acid produced maintains stoichiometry with that of the charged resin. The macroporous ion exchanging resins that are currently available have a capacity of change close to two equivalents per liter.

If the direction of circulation of the solutions within the column is inverted by feeding an acid solution through the upper part of the column and extracting saline solution through the lower part, the ion exchange zone shifts progressively downwards. The resin i.s regenerated at the same time and a saline solution is produced in a quantity which maintains stoichiometry with the regenerated resin.

The object of the invention is a procedure for obtaining salts and acids in solution based on ion exchange with ion

I

i-

-L

4 exchanging resins in separate stages. In particular, the present invention utilises a moving bed ion exchange system.

Examples of the use of earlier moving bed ion exchange systems can be found in GB-1212727, GB-A-2027610, GB-A- 2107602 and WO 79/00920. However, when using these earlier systems, high yields of desired salt and/or acid solutions are not obtained. The present invention seeks to overcome this problem.

According to the present invention there is provided a process for obtaining a salt and/or an acid in solution from another available one, by ion exchange utilising ion exchanging resins, wherein the stages of charging and regeneration of the resin are carried out in separate receptacles of column shape, by cyclic transference of amounts of resin between two columns, and providing an intermediate rinse with water in order to remove a solution which floods the transferred amounts of resin, characterised in that the first stage of the process comprises charging, in a first ion exchanging column, a volume of ion exchanging resin with the cation corresponding to the salt which it is desired to obtain in a second ion exchanging column, by circulating through the first ion exchanging column a solution of a salt, the cation of which salt corresponds to that of the salt which it is desired to obtain in said second ion exchanging column and the anion of which salt corresponds to that of the acid or salt which it is desired to obtain in the first ion exchanging column; and the second stage of the process comprises regenerating, in a second ion exchanging column, the resin charged in the first stage, by circulating through the second ion exchanging column a solution of a salt or acid, the anion of which salt or acid corresponds to that of the salt which it is desired to obtain in said second ion exchanging column and the cation of which salt or acid corresponds to that of the salt or acid which it is desired to obtain in the first ion exchanging column, such that the relative amounts of the fed solutions are selected so as to carry the r corresponding ion exchanging zones into the ion exchanging columns near the opposite end of said columns, without those zones going outside of the columns, and such that in each cycle of operation and from each ion exchanging column an equivalent amount of resin is extracted, said amount being that required for carrying said ion exchanging zones from one end to the other end of the columns and without those zones going outside of the ion exchanging columns.

High yields of desired salt and/or acid solutions are obtained because the exchanging zones or interfaces are never extracted from the columns do not go outside of the columns), unlike the earlier processes.

The present invention also gives rise to the advantages which are mentioned in the following paragraphs.

The present invention permits the design Of productive units susceptible of a high degree of automation. It also allows independent regulation of the two stages of the process. It also makes it possible to carry out the ionic exchange processes at temperatures close to the atmospheric temperature with a minimal energy requirement. The units can also be operated at much higher temperatures providing the conditions are not damaging for the resin.

The utilisation of macroporous ion exchanging resins based on the copolymers of styrene and divinylbenzene sulphonates, which are highly resistant to osmotic shocks, makes it possible to operate with concentrated solutions without altering the structure of the resin, with the advantage that crystalline products can be obtained. At the same time, these types of resins are very resistant to attrition, thus they can resist a large number of cycles and can be handled in the process without experiencing any significant deterioration. The small proportion of fines which are inevitably produced in handling the resin are normally separated in its washing operations.

6 As stated above, the preferable ion exchanging resin is a cationic resin formed by a copolymer of styrene and divinylbenzene sulphonate, which is in the form of spheres of 0.6 mm average diameter. However, other types of resins can also be utilised in the present invention. For example, anionic ones can be used so long as they are solid, have a similar form and are resistant to the physical-chemical conditions of the process.

The present invention will now be described by way of examples and with reference to the accompanying drawing, in which: Figure 1 is a schematic representation of an example of organisation of the devices and elements involved in a first form of execution of the present invention; and Figure 2 is a schematic representation, similar to the above, of a second form of execution of the present invention.

Basically the present invention comprises conducting the processes of charging and regeneration of the resin in two separate stages and in different columns.

Referring to Figure 1, the process of charging the resin with a salt in solution is carried out in a first column At the same time, an acid solution corresponding to the salt is generated.

The column as it is represented schematically, is a receptacle of a cylindrical form and is arranged vertically.

In its upper and lower ends are isolation valves and resin moving valves. Near the lower end, there is a conduit or tubulure (11) for introduction of saline solution. Near the upper end, there is another condu.it or tubulure (12) for extraction of the acid (o1 saline) solution, which is I 7 generated by the present process. Both the tubulures (11, 12) are connected to internal distributors of liquids that are intended to guarantee a uniform flow of the solutions in the whole section of the column while they are being circulated through the resin. The distributors are designed to permit the passage of liquids, but are also designed to retain resin. They are arranged to permit movement of the resin through the column.

The dimensions in diameter and height of the column (10) may vary between wide limits which are dependent upon the capacity of production which is projected.

For greater clarity of explanation, the description of the procedure for the charging stage of the resin will be made on the basis of utilising a solution of potassium chloride (Kcl) as a saline solution. Potassium chloride (KC1) is prepared at room temperature (20 0 C) as a 3N solution. The KC1 solution is free of solid or dissolved impurities, which can disturb the operation of the present invention or damage the resin, In the first stage of the procedure covered by the present invention, one begins by filling the charging column with a quantity of an ion-changing resin that was previously contained in a vessel The ion-exchanging resin is in an acidic form because it was flooded with a solution of 3N hydrochloric acid (HC1) when contained in the vessel (13).

When the column (10) is full of resin and the resin moving valves are closed, one proceeds to feed the 3N KC1 solution through the lower tubulure (11) of the column and to extract the solution of hydrochloric acid through the upper one (12).

The feeding rate of the 3N KCI saline solution is regulated at the equivalent of a volume of resin contained in the column by the hour. The condition which defines the flow of the saline solution is that required to achieve a short and r 8 well differentiated zone of ionic exchange inside the column, above which only coexist the resin in acid form (RH) and the solution of the acid corresponding to the salt which is introduced, and under which only coexist the resin in charged form (RK) and the solution of the salt which is introduced. This condition can vary and is dependent upon inter alia the concentration of the salt, the physicalchemical affinity of the cation of the salt (K to the resin in relation to that of the one it replaces (H and of the granulometric curve of the resin.

As the salt solution is fed into the column, the ionic exchange zone shifts from the bottom of the column upwards, generating a quantity of hydrochloric acid in solution equivalent to that of the resin which is being charged.

When the zone of ionic exchangu arrives at the proximity of the upper tubulure from whence the solution of hydrochloric acid is extracted, the feeding of the salt solution is stopped. In this way all the resin located in the column below the zone of ion exchange is charged (i.e.

in form of RK).

Once the resin contained in the column (10) is charged (i.e.

in form of RK), the admission and outlet valves for solutions are closed and one proceeds to circulate the volume of regenerated resin through the column corresponding to one cycle. The volume of regenerated resin can be contained in' the vessel (13) during the circulation step.

The vessel (13) is arranged above the column (10) and connected to it by a valve. The resin is then flooded in the column (10) by an acid solution, which is derived from the process itself. The acid solution enters the column through pipes as will be explained later. At the bottom of the column, charged resin in form of RK) goes out through a valve.

In this last operation, the ion exchange zone which was initially near the upper tubulure (12) descends as the resin S I 'ii* 1 9 circulates until it is located above and near the lower tubulure At that time, the circulation of resin through the column is stopped and the corresponding valves are closed. The volume of circulating resin is kept at a constant in each cycle to facilitate the operation.

Next, the intake and outlet solution valves are opene and saline solution i, fed until the ion exchange zone locates itself in the zone next to the upper tubulure (12) of the column.

Therefore, by following the first stage of the present procedure and the repeating cycles, the regenerated resin (RH) is transformed into charged resin (RK) and the salt solution which is fed is transformed into corresponding acid solution.

The total quantity of salt, in solution form, fed in each cycle is that which is necessary to charge the quantity of resin which is circulated, plus the amount of salt that goes out the column accompanying the resin in each cycle. The quantity of the acid, which is in solution form and which is moved in each cycle, coresponds stoichiometrically to the quantity of resin which is charged, plus the quantity of acid which enters the column flooding the resin in each cycle.

Ion detectors are installed in order to assure that the ion exchange zone is moved in the column in each cycle within the established limits and to guarantee that only the acid solution goes out of the column without being contaminated with legenerated resin (RH) The signals of these detectors are utilised to adjust the quantity of salt solution fed in each cycle.

The first stage of the procedure covered by the present invention is not only valid for transforming a salt into the corresponding acid, but also serves to transform one v"lit

P"

into another of the same anion. In this case, the resin which is fed into the column (10) in each cycle must be charged with the cation corresponding to the salt which it is desired to obtain. Thus, if the resin is charged with sodium in the form of RNa), and potassium chloride (KC1) solution is fed into the column, a sodium chloride solution (NaCl) and a potassium charged resin (RK) will be obtained. In this case, the limit of concentrations of the solutions involved is set by the solubility of the less soluble salt.

In the procedure described above, the resin and the solutions circulate in a counter-current fashion, in that the resin circulates downwards and the solutions circulate upwards within the column However, this direction can be reversed. As a criterion to establish the direction of circulation, it is preferred that the less dense solution of the iopn exchange zone be.in the high part of the column in order to avoid disturbances of the ion exchange zone originating from differences of densities.

As stated above, the charged resin in the form of RK) is flooded by the solution of the salt employed to charge it as it comes out of the column (10) in each cycle. However, before transferring this resin into a second column in order to carry out the second stage of the process, it is necessary to separate, by suitable means, the anion of the salt from the resin in order to avoid saline contaminations in the products to be obtained. One way of achieving this is shown in Figure 1. In this case, the resin, accompanied by the saline solution which is extracted from the column is transferred to a vessel which is in th, fGrm of a vertical columtn. The vessel (14) is equipped with a double bottom in the form of a grating which retains the resin but allows the liquid materials to pass through.

First, the salt solution is drained off though the pipe The resin is then washed with water, which enters though pipe until the salt is eliminated. The diluted C 11 solution, which is extracted through the pipe is used to dissolve more salt and it is reutilised in the process once the concentration is adjusted.

The washed and drained resin in the vessel (14) is now available for utilisation in the second stage of the procedure. For this purpose, it is first transferred into a vessel (23) in a salt solution that can be obtained from the column (20) (see later). The salt solution enters the vessel (14) through the pipe (27), The second stage of the present invention comprises an ion exchange between the charged resin from the first stage of the present invention and an acid or salt solution having a different anion and cation from those used in the first stage. The ion exchange process is performed in the column which is of a similar design and construction to that of the first column The operating mechanism of the second stage is similar to that of the first but reversed. The volume of resin, corresponding to each cycle and resulting from the first stage, is introduced into he column (20) and then flooded with an appropriate salt solution, At the same time, as the charged resin (RK) is introduced though the lower part of the column, the same volume of regenerated resin is extracted thought the upper part, In each cycle, the zone of ion exchange which is established is shifted from the lower part of the column to the upper part.

When the ion exchange zone is in the upper part of the column (20) and the resin moving valves are closed, an acid solution is fed though the upper tubulure (21) at the time that the corresponding salt solution is extracted though the lower tubulure In this way the ion exchange aone is shifted to the lower part of the column where it was before the resti was introduced, and a quantity of salt equivalent to the volume of regenerated resin is generated.

aesired to obtain in a second ion exchanging column, by circulating through the first ion exchanging column a solution of a salt, the cation of which salt corresponds to 2

I

12 The molar concentration of the acid which is fed corresponds approximately to that of the salt which is obtained, and it is limited by the concentration of saturation of the most insoluble compound at the temperature of operation.

If a solution of a salt is used to regenerate the resin, the same exchange mechanism is carried out and a resin, in form of the corresponding salt, is obtained instead of a resin in acid form (RH).

The circulation of resin and solutions in each cycle can be synchronisec. in the two stages of the process.

The regenerated resin which comes out of the column (20) in each cycle is flooded by an acid or salt solution employed for its regeneration. Before transferring this resin to the first column Ln order to conduct the first stage of the process and close the run of the resin, it is necessary to separate out, by suitable means, the solution which floods it. In order to achieve this, the resin and the solution which floods it are transferred to a vessel (24) which is of a column shape and of a design similar to the vessel \14) previously described. Afterwards, the solution which is recycled, through the pipes (25) is drained and the resin is washed with water, which enters through entrance until the anion of the solution is suitably eliminated, The washed and drained resin is then conveyed to the vessel (13) by means of the acid (or salt) solution obtained in the column which enters through the pipe The resin is then available to pass to the column (10) for the first stage of the process.

A second way of conducting the procedure covered by the invention is illustrated in Figure 2. In this case, the salt solution can be separated from the resin ay displacing l I, place by the shifting of one solution by the other, without the solution mixture zones in said columns going outside of said solution shifting columns.

II 1 -1 13 the solution with another salt solution obtained in the second stage of the process.

The charged resin in form of (RK) that comes out from each cycle from a first column (100) is transferred to a vessel (130) in column shape and with design char,,cteristics similar to those of the column (100). Afterwards, there is fed into that vessel (130), through a lower tubulure (140), a volume of salt solution equal to the volume of salt solution transferred with the resin coming from the column (100) i In this case, the salt solution has been obtained in a second column (200) in the second stage of the process.

The corresponding volume of salt solution that entered with the resin is simultaneously extracted through an upper tubulure (150) from the vessel (130).

Between the solutions of salts in the vessel (130), a zone of saline mix is established in which the two anions have inverted gradients of concentration and above which the resin only coexists with the solution of salt which is fed into the vessel. The resin does not suffer transformations in this phase.

This zone of saline mixture is shifted in each cycle from one end to the other of the vessel (130) within the limits established so that it never goes out of the vesscl with the materials that are extracted. When the movement of the resin is started, the saline mixture zone in the upper par: of the vessel (130) is made to coincide with this movement and t'ie vessel is always kept full of resin flooded by the saline solutions. In this phase of the circulation cycle, the resin that comes out of vessel (130) enters the column (200) through a valve..

In the second stage of the procedure, the solution can be separated from the resin by shifting with another solution.

In this case, the operation is performed in a vessel (230), the design and function of which are similar to thoe of the 5845/3 )I 14 vessel (130) previously described. In each cycle, the corresponding resin that comes out of the column (200) is transferred to the vessel (230) though the lower part. At the same time, an equal volume of resin comes out though the upper part. The shifting of the solution, which enters the vessel (230) with the resin, is done by feeding through the upper tubulure (250) in each cycle and in a countercurrent sense with the resin. The equivalent quantity of the acid (or salt) solution produced in the column (100) in the first stage of the procedure can be fed into the vessel (230) via the tubulure (250). The shifting mechanism for the solution is similar to the one that takes place in the vessel (130).

The resin that comes out from the vessel (230) in each cycle is received in a vessel (300). It is then moved to another feeder vessel (.310) which feeds the column (100). In this particular example of the present invention, the movement of the resin corresponding to each cycle is synchronised among all of the elements or equipment, and the resin is measured and driven from the vessel (310)., In Figure 2, the assignment of numerical references to elements of the diagram (tubulures, pipes, valves, etc.) whose function can be understood from the explanation and from the similarity among stages and illustrated arrows, have been omitted.

EXAMPLE 1 i SA productive unit designed to obtain potassium nitrate (KN03) and hydrochloric acid (HC1) from potassium chloride (KC1) and nitric acid (HNO 3 with an approximate capacity of 5,000 MT per year of potassium nitrate, would have the following basic characteristics: i t Iwnr Dimensions of the columns: Diameter 1.2 m; height 5 m.

S Volume of resin moved in each cycle: 1 m Number of cycles per hour to be done: 3.

Approximate quantity of ion changing resin in circuit: 15 m.

In the first stage of the process, the resin is charged with potassium ion charged to RK) by means of a solution of potassium chloride (KCl) 3 N. Hydrochloric acid is simultaneously obtained in solution at a concentration of 2.8 N. In the second stage of the process, the resin is generated to its acid form (RH) with nitric acid solution in concentration of 3 N. Potassium nitrate (KNO 3 is obtained simultaneously in solution of approximately 3 N concentration.

EXAMPLE 2 In the same production unit as Example 1, potassium nitrate (KN0 3 can be obtained in solution, from sodium nitrate (NaNO 3 The resin is regenerated in the second stage with a solution of sodium nitrate (NaN0 3 of 3 N concentration.

In the first-stage, if the resin is charged with potassium chloride (KCl) solution of 3 N concentration, a solution of sodium chloride is simultaneously obtained of 3 N concentration.

EXAMPLE 3 In the same production unit as Example 1, monopotassium phosphate can also be obtained in solution from a solution of monocalcium phosphate. For this, the resin is charged in the first stage with a potassium chloride (KCl) solution of 3 N concentration and, at the same time, a solution of hydrochloric acid is obtained. In the second stage of the process, the resin is regenerated with a solution of monocalcium phosphate and a solution of monopotassium phosphate (KH 2 P0 4 is obtained.

x I Iii- 16 EXAMPLE 4 In the same production unit as in Example 1, phosphoric acid -an also be obtained in solution from a solution of luonocalcium phosphate. The resin is charged for this purpose with a potassium chloride Ca(H 2

PO

4 2 solution in the first stage, simultaneously obtaining phosphoric acid

(H

3

PO

4 in solution. In the second stage, the resin is regenerated with hydrochloric acid (HCl) in solution.

These examples are illustrative of the fact that the procedure covered by the invention applies to an infinite number of combinations for obtaining salts and soluble acids of industrial and commercial value, from other available salts and acids.

Claims

2. A process according to claim 1 wherein the exchange solutions are fed through an end of the columns so that there is an increasing density of solutions towards the bottom of the columns.
3. A process according to claim 1 or 2 wherein the equivalent amounts of resin, that are cyclically transferred between the two ion exchanging columns, are previously submitted to a solution shifting process in two solution shifting columns, each connected to a respective ion exchanging column, there being substituted into those solution shifting columns a shifting solution which floods the transferred amount of resin with the exchange solution that will be used in the next ion exchanging column according to the operation cycle, said substitution taking place by the shifting of one solution by the other, without the solution mixture zones in said columns going outside of said solution shifting columns.
4. A process according to claim 3 wherein the solution mixture zones, that are established when the two shifting solutions are introduced into said solution shifting i columns, move cyclically between one end and the other end of the columns without going outside of said solution shifting columns. A process according to either claim 3 or 4 wherein the shifting solution, which is fed into the repective solution shifting columns, is the solution produced in the ion exchanging column from which the resin will be transferred in each cycle. 19
6. A process according to any one of claims 3 to 5 wherein the shifting solutions are fed In said solution shifting columns through an end of the columns so that tihere is an increasing density of solutions towards the bottom of the columns.
7. A process according to any one of the preceding claims wherein the flow of the solutions, which are fed into the ion exchanging and solution shifting columns, Is regulated to values close to a bed volume of resin per hour based upon the affinity of the resin to the cation, the concentration and density of the solutions, the granulometry of the resin and the temperature of operation.
8. A process according to any one of the preceding claims wherein the columns employed in the process are all of cylindrical shape and have a relation of diameter to height of at least one to five.
9. A process for obtaining a salt and/or an acid in solution from another available one, substantially as hereinbefore described and with reference to either Figure 1 or Figure 2. A salt and/or an acid whenever obtained by the process according to any one of claims 1 to 9. DATED this NINETEENTH day of MARCH 1991 Industrial Quimica Del Nalon, 7.A., Empresa Nacional De Fertilizantes, S.A. Patent Attorneys for the Applicant SPRUSON FERGUSON KXN:1299y